"I can't remember the last time we didn't sell out. It's been that long," Dumontier added.

Threats of more student protests -- and an anonymous security threat -- forced organizers to cancel Thursday's free opening day of the event, where spectators have traditionally had access to the Circuit Villeneuve.

"We did receive some direct threat on the event," Dumontier told the media here.

Riot police in Montreal arrested more than 20 anti-capitalist demonstrators after dozens of protesters showed up at a Grand Prix cocktail event, condemning the Formula One event as "polluting, sexist and thieving."

"Police are protecting the Grand Prix and arresting students," protesters shouted, referring to a spate of arrests earlier in the day of students accused of mischief and vandalism linked to the long-running unrest in the province.

Quebec university students have protested for four months over government plans to hike tuition fees by 75 percent. The unrest has morphed into a broader campaign against perceived government corruption and a mishandling of environmental policies.

"We come here, it's a sensational event for the whole season as one of the top few Grands Prix of the year; fans-wise, drivers, mechanics, photographers, journalists, everyone loves coming here.

"Obviously I'm not completely up to speed with what's going on. Some of the students are not happy with certain things," he said.

"I'm sure that the weekend will go well. We want to put on a very, very good weekend for everyone in Montreal and Canada and that's the focus for everyone in Formula One."

Briton Jenson Button said of the open house cancellation: "I think it's just a precautionary thing. It's the start of the weekend, and we hope for a very exciting weekend and this is a big weekend for Formula One but also for Montreal."

Brazilian Felipe Massa didn't hide his disappointment.

"We want to see all the fans, all the young people, students, everybody, we want to see them here with us. I hope everything becomes normal with this situation. For sure, for us we feel sad for this situation."

Quebec Premier Jean Charest, a staunch defender of the Grand Prix, expressed his anger at the direct threats waged against the race.

"When we attack the Grand Prix, it's not the Quebec government that people are assaulting, it's all Quebecers," Charest said.